Treatment of gases in electric furnaces.



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TREATMENT OF GASES IN ELECTRIC FURNACES.

APPLICATION FILED FEB. 14. ms.

1,263,390. Patented vApr. 23, 1918.

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TREATMENT on GASES I Original application filed August Specification of Letters Patent.

29,1916, Serial N0.

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Patented Apr. 23, 1918. 117,492. Divided and this application filed February 14, 1918. Serial N0. 217,284.

To all whom it may concern:

Be it'known that I, EMIL EDWIN, asubject of the King of Norway, residing at a have been treated in electric furnaces, and is f gases, leaving the furnace.

of pure oxygen one high pressure in the furnaces.

late time; to time supplied.- Also in this case a a division of my application Serial Number 117 ,492, filed August 29, 1916.

In'the processes of nitrogen combustion, the supplied electric ener is but imperfectly utilized. Only the east part-of the energ is directly transformed into chemical energy in the formation of nitrogen oxids, while the bulk is obtained as heat in the hot The conditions may be improved to some degree b using greater yield'of nitrogen oxids is obtained relatively'to the expenditure of energy, but the advantage so'obtained is in great measure counterbalanced by the complication that a compressor plant with consequent expenditure of energy is required to supply the air-under pressure to the furnaces. nother method of obtaining an increased yield of nitrogen oxids consists in usin a gas mixture richer in oxygen than the air, most profitably a mixture conta1mn equal volumes of oxygen and nitrogen. 11 consideration of the 'cost arising from the preparation is then bound to combine the furnaces with the absorption plant and auxiliary apparatus into a closed sysmm, in which the gases permanently circw the quantities of gaslused being" from compressor is requlred in orderto maintain the differences of pressure that are necessary for the circulation of the-gases in the systhe same is thecase when both are simultaneously made use of1n working hen athe yield the closed system under pressure with air rich in oxygen. I

When using a closed system, one has the further possibility of efiectin also the absorption of the nitrogen oxid s under pres- V, sure. This involves the important advantage, that the absorption lant may be given far less dimensions and consequently be much cheaper. This advantage may be utilized still more by maintaining the absorption system under even higher pressure than the'furnace's, but one faces then again the necessity of using a compressor for producing this higher pressure, so that also in this case the profit is to be purchased at expend? ture of energy.

Considering on the other hand the energy contained as heat in the hot gases leaving the furnace, it is evident that this, energy "may be utilized in different ways,-for instance for the production of steam in ass ing the gases through steam-boilers. owever, a considerable portion of the heat content, particularly the heat remaining in the gases after their having been cooled down to 250-300 (3., cannot be utilized in this way, a

compressoras nearly isothermally as feas-' 'ible, it will be within the range of possibility with the normal efiiciencles of such machines to save 5* or even more of the coin? pressor work, so that only the remaining or less is to be supplied from external sources, for "instance from an electromotor.

In order to keep'the pressure as constant as possible, which is essential to the stability of the flame, it is of great importance that the .velocity of the compressor should c01- respond to any variations in the velocity of the turbine,due to variations in the'quanplant.

" I-have shown a tity of gas delivered by the furnace, the pressure, and rate of expansion. Thls may be realized in' using ajrotary compressor placed directly on the driving shaft of the turbine. Small variations of pressure will moreover be equalized on account of the relatively large volume of the absorption The manner in which the invention is carried out is shown diagrammatlcally 1n the annexed drawing, in which a indicates the furnace, b a device, for instance a boiler, for cooling the hot furnacegases-under s1- multaneous utilization of a great v deal of. their heat, a is the translating devlce operating by continuous expanslon, such as a hot-air turbine, cl the rotary compressor placed on the turbine shaft and e the absorptionplant. i I, p

closed system in which the absorption plant stands under. higher pressure than the furnace. In this casethe gases from the furnacefirst, after givmg up the greater portion of their heat, for ex-' ample to the steamboiler b then pass to a, heat exchanging device '7, where they are cooled and then to the compressor d, which brings the pressure up to that-bf the absorption plant 6. The cooler gases lssuing from the latter return through 1 thesecond J cooling stage in the heat exchanger f inwhich theyare heated by means of the above mentioned gases from b and then pass on tothe turbine, where the gases expand to the pressure prevailing in the-furnace.

The oxygen and-the nitrogen to replace the quantity of combined oxygen and nitrogen withdrawn from circulation in the closed system by absorption in e are introduced into the system under pressure. Inorder to do this, use is made of an electric.-

motor driven compressor, not indicated.

The arrangement above described, is mainly, destined for the process of nitrogen. combustion in electric furnaces, but it is understood, that the, underlying principles may easily be modified for the use in other processes of analogous nature, 13. e., processes working with a system in which hot gases-are circulating and where the difi'erent parts" of the system have considerable difierences of pressure. i

So. for instance the invention may be usedin the manufacture of aluminum nitrid froml alumina, carbon and nitrogen.' When" in this andother similar processes circulating.

nitrogen is used, it will be necessary'td'in 'ing to that illustrated. it

- sert in the system a device for eliminating the carbon monoxid from the "gases, 'before 5' the latter are re-used, and the system of such processes is then on a principle correspond- Iclaim-' of utilizing the heat entranslating device to furnace electric furnaces of nitrogen combustion, consisting in that the gasesleaving the absorption plant, which latter stands under higher pressurethan the furnace, are first: conducted through a heat exchanging apparatus in which the relatively cool gases from the absorption plant are preheated by the hot-furnace gases, and are then subjected to a drop of pressure between theabsorption plant and the furnace thereby being caused to transform their heat energy .into mechanical work in a hot-air turbine, which latter drivesa rotary compressor working approximatel 4 at the same difference of pressure as t e turbine andsupplying the circulating gases to the absorption plant.-'

2. The method of utilizing the heat .energy of gases that have been treated in an electric arc furnace, which comprises causing the gases to circulate in a, closed system between an electric arc furnace and an absorber maintained under pressure higher that the furnace, cooling the-gases after the cooler gases to a pressure higher than ,the furnace pressure, absorbing a portion ,of the gases at such higher pressure and con-' tinuously expanding said gases'through a ressure, said continuous expansion being su stantially in synchronism with the aforesaid compression, and supplying the expanded gases ',to said furnace; Y 1

4:. The method of utilizing .thehe'at energy of electric arc furnace gases, which comprises discharging ,the gases from the furnace through a heat absorber, compressing the cooler gases to pressure higher than the furnace pressure, absorbing a portion of said gases at such higher pressure, reheating the residual gases and continuously expanding'themtc furnace pressure through a translating device operating, in; asynchronism with the compression and delivering the expanded residual gases to, the fufnace. 5. The. method of utilizing; the heat. en ergy of electric arc fumes ases1 which comprises absorbing heat from 'e gases discharged from the furnace in two, stages,

compressing the cooled gases" to a pressure o higher than their initial pressure, absorbing a portion of said gases at such hlgher pressure, reheating the gases 1n one of said cooling stages, causing a continuous expansion of said residual gases through a translating device operating in synchronism with said compression down to furnace pressure, discharging said gases into the furnace and introducing compressed gases into the cir cuit suflicient to compensate for the absorption.

6. The method of utilizing the heat energy of electric arc furnace gases, which comprises absorbing heat from the gases discharged from the-furnace in two stages, compressing the cooled gases to a pressure higher than their initial pressure, absorbing a portion of'said gases at such higher as my invention, I have 

